It's a sad stat...because graduation rates are so abysmally low in so many areas of this country. Something like a third of high school students never graduate. Of those attending junior college, less than half ever graduate with a full, 4-year degree.
The "rate" number is calculated as the actual number of students flipping that tassel from left to right on their mortarboards...divided by the total number of students who initially enrolled in that class, believing they'd graduate 4 years later.